Among the apparatus for handling and receiving speech signals or audio signals, there is video equipment, such as a television, or audio equipment, such as a radio, CD player, MD player or a video tape recorder (VTR). As a method for communication of signals employed in such apparatus, such as a video tape recorder (VTR), with other equipment, a serial digital interface (SDI) format is proposed by the Society of Motion Picture and Television Engineers (SMPTE) in Proposed SMPTE Standard for Television-10-bit 4:2:2 Component and 4fsc Composite Digital Signals Serial Digital Interface (SMPTE-295M, 1994 Revision-Seventh Draft, Feb. 16, 1994) as a standard for digital audio and video signals. This SDI standard is basically a standard for signals governed by D-1 or D-2 formats for digital signals. The disclosure of Proposed SMPTE standard SMPTE-295M is hereby incorporated herein by reference.
FIG. 1 shows a schematic arrangement of the SDI format which represents the application of D-1 format signals.
An upper part of FIG. 1 shows a frame format of a frame made up of 1716 samples in the horizontal direction and 525 lines in the vertical direction. Digital video signals are placed in a first field active video section AVC.sub.1 of 1440 horizontal samples and 244 vertical lines and a second field active video section AVC.sub.2 of 243 lines. Specifically, the first field active video section AVC.sub.1 is a digital video signal of odd fields and the second field active video section AVC.sub.2 is a digital video signal of even fields. Ahead of the first field active video section AVC.sub.1 and the second video active section AVC.sub.2 are respectively inserted 9-line vertical blanking section VBK.sub.1, VBK.sub.2 and 10-line optional blanking sections OBK.sub.1, OBK.sub.2. Ahead and back of the first field active video section AVC.sub.1, second video active section AVC.sub.2, vertical blanking sections VBK.sub.1, VBK.sub.2 and the optional blanking sections OBK.sub.1, OBK.sub.2 are inserted a 4-sample start synchronization code SAV indicating the start of an active line and a 4-sample end synchronization code EAV indicating the end of the active line. Between the start synchronization code SAV and the end synchronization code EAV are placed 268 samples of an ancillary data section ANC which are ancillary data for horizontal blanking. A mid part of FIG. 1 indicates a signal of a frame format shown at the upper part of FIG. 1 in a line format having a width of 10 bits. For transmitting signals of the SDI format, parallel/serial conversion and encoding of the transmission channel are carried out as shown at a lower part of FIG. 1, and the signals are transmitted as serial signals having a data rate of 270 Mbps.
Although data transmission by the SDI format is achieved at a high speed, the SDI format is not suited as a transmission channel for variegated data, while it is possible to transmit only a limited type of data (information). Specifically, the data sorts capable of being transmitted include one channel of picture signals (or video signals) and 8 channels at most of speech signals (or audio signals) as the base band digital audio signals. Thus the SDI format is not suited to transmission and reception of plural channels of the same sort of data or channel multiplication for coping with transmission and reception of plural sorts of data. On the other hand, data other than picture signals or speech signals are transmitted over a physically separate channel. In addition, the SDI format basically takes account only of one-to-one unidirectional data transmission.
In general, when simultaneously transmitting plural sorts of data, the method of providing a data transmission channel for each data sort is simple and easy, it being unnecessary to carry out data processing for transmitting excessive data. However, this presents a problem in efficiency and economic profitability in connection with cost involved in the entire data transmission system, cost involved in the data transmission channel, or labor in maintenance or extendibility of the data transmission system.
In local networks employed in data communication (LAN), especially in information processing equipment, data communication channels, such as Ethernet or token ring, have become popular in use. However, such data communication channel inherently has been developed as a data communication channel handling temporally discrete data, such as packet data employed for an electronic computer, while it is not suited as a transmission channel for temporally continuous data, such as picture/video or speech/audio signals, which require maintenance of a temporal relation between the transmitting and receiving sides. On the other hand, the data transmission rate of the data communication channel is rather low and is not suited to transmission of picture signals which require wide frequency range, or bandwidth.
The technological tendency in the near future is to digitize all kinds of the information, inclusive of the picture/video and speech/audio data, and to treat the information simply as a bitstream irrespective of the data type. Above all, in the future digital integrated network, exemplified by the AM technique, all kinds of data are transmitted as a multiplexed bitstream. If such technical tendency is taken into consideration, the SDI format currently standardized for picture signal transmission is not fully satisfactory, while there lacks at present a particular data format for multiplexing and transmitting various data and control signals among plural communication equipment.